Building and construction applications in which materials such as concrete, metal, and glass are used typically employ joint systems that accommodate thermal expansion and/or seismic movement of the various materials thereof. These joint systems may be positioned to extend through both the interior and exterior surfaces (e.g., walls, floors, and roofs) of a building or other structure. In the case of an exterior joint in an exterior wall, roof, or floor exposed to external environmental conditions, the joint system may also, to some degree, resist the effects of such conditions. As such, most exterior joints are designed to resist the effects of water. In particular, vertically-oriented exterior joints are designed to resist water in the form of rain, snow, ice, or debris that is driven by wind. Horizontally-oriented joints are designed to resist water in the form of rain, standing water, snow, ice, debris such as sand, and in some circumstances several of these at the same time. Additionally, some horizontal systems may be subjected to pedestrian and/or vehicular traffic and are designed to withstand such traffic.
In the case of interior joints, water tightness aspects are less of an issue than they are in exterior joints, and so products are often designed simply to accommodate building movement. However, interior horizontal joints may also be subject to pedestrian traffic and in some cases vehicular traffic as well. Particularly with regard to joints in horizontal surfaces, cover plates can be fitted over the joints to allow for the smooth movement of traffic over the joint and/or to protect the material of the joint from the effects of the weather.
It has been generally recognized that building joint systems are deficient with respect to fire resistance. In some instances, movement as a result of building joint systems has been shown to create chimney effects which can have consequences with regard to fire containment. This often results in the subversion of fire resistive elements that may be incorporated into the construction of a building. This problem is particularly severe in large high-rise buildings, parking garages, and stadiums where fire may spread too rapidly to allow the structures to be evacuated.
Early designs for fire resistive joints included blocks of mineral wool or other inorganic materials of either monolithic or composite constructions. Field-applied liquid sealants were often used in these joints. In general, these designs were adequate for non-moving joints or control joints where movements were very small. Where movements were larger and the materials were significantly compressed during the normal thermal expansion cycles of the building structure, these designs generally did not function as intended. Indeed, many designs simply lacked the resilience or recovery characteristics for maintaining adequate coverage of the entire joint width throughout the normal thermal cycle (expansion and contraction) that buildings experience. Many of these designs were tested in accordance with accepted standards such as ASTM E-119, which provides for fire exposure testing of building components under static conditions and does not take into account the dynamic nature of expansion joint systems. As described above, this dynamic behavior can contribute to the compromise of the fire resistance properties of some building designs.
Underwriters Laboratories developed UL 2079, a further refinement of ASTM E-119, by adding a cycling regimen to the test. Additionally, UL 2079 stipulates that the design be tested at the maximum joint size. This test is more reflective of real world conditions, and as such, architects and engineers have begun requesting expansion joint products that meet it. Many designs which pass ASTM E-119 without the cycling regime do not pass UL 2079. This may be adequate, as stated above, for non-moving building joints; however, most building expansion joint systems are designed to accommodate some movement as a result of thermal effects (e.g., expansion into the joint and contraction away from the joint) or as a result of seismic movement.
Both expansion joints and fire resistive expansion joints typically address either the water tightness (waterproof or water resistance) aspects of the expansion joint system or the fire resistive nature of the expansion joint system, as described above, but not both.
Water tight expansion joints exist in many forms, but in general they are constructed from materials designed to resist water penetration during the mechanical cycling caused by movement of the building due to thermal effects. These designs generally do not have fire resistant properties in a sufficient fashion to meet even the lowest fire rating standards. Indeed, many waterproofing materials act as fuel for any fire present, which can lead to a chimney effect that rapidly spreads fire throughout a building.
Conversely, many fire rated expansion joints are not sufficiently water tight to render them suitable for exterior applications. Many designs reliant upon mineral wool, ceramic materials and blankets, and intumescents, alone or in combination with each other, have compromised fire resistance by coming into contact with water. Additionally, as noted above, many fire rated designs cannot accommodate the mechanical cycling due to thermal effects without compromising the fire resistance.
This has resulted in the installation of two systems for each expansion joint where both a fire rating and water resistance is desired. In many cases, there simply is not sufficient room in the physical space occupied by the expansion joint to accommodate both a fire rated system and a system capable of providing waterproofing or water resistance. In instances where the physical accommodation can be made, the resultant installation involves two products, with each product involving its own crew of trained installers. Care is exercised such that one installation does not compromise the other.
Many systems also employ on-site assembly to create a finished expansion joint system. This is arguably another weakness, as an incorrectly installed or constructed system may compromise fire and water resistance properties. In some cases, these fire resistant expansion joint systems do not employ cover plates and are instead invasively anchored to the concrete substrate. Over time, the points at which such systems are anchored are subject to cracking and ultimately spalling, which may subvert the effectiveness of the fire resistance by simply allowing the fire to go around the fire resistant elements of the system. Without cover plates over the joints, fire in these cases would not be contained within the joints.
Also, many expansion joint products do not fully consider the irregular nature of building expansion joints. It is quite common for an expansion joint to have several transition areas along its length. These may be walls, parapets, columns or other obstructions. As such, the expansion joint product, in some fashion or other, follows the joint. In many products, this is a point of weakness, as the homogeneous nature of the product is interrupted. Methods of handling these transitions include stitching, gluing, and welding. All of these are weak spots from both a water proofing aspect and a fire resistance aspect.